You compare life totals with each of your opponents when Timely Reinforcements resolves. At that time, if you have less life than an opponent, you'll gain 6 life. Similarly, you compare the number of creatures you control with the number of creatures each opponent controls when Timely Reinforcements resolves.

9/22/2011

In a multiplayer game, you consider each opponent. If you have less life than one of your opponents and fewer creatures than one of your opponents (although this may be a different opponent), you'll get both bonuses.

9/22/2011

In a Two-Headed Giant game, you'll compare your team's life total with the opposing team's life total. You'll then compare the number of creatures you control (ignoring creatures your teammate controls) to the number of creatures each opponent controls separately.